Life Cycle Assessment of Electricity Generation from Low ... · Thomas Gibon and external contact Yves Ladam for their academic and technical guidance. Thanks to the Industrial Ecology

Life Cycle Assessment of Electricity Generation from Low Temperature Waste HeatThe Influence of Working Fluid

Lijun Bai

Master in Industrial Ecology

Supervisor: Edgar Hertwich, EPTCo-supervisor: Yves Ladam, SINTEF Energy Research

Department of Energy and Process Engineering

Submission date: July 2012

Norwegian University of Science and Technology

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Life Cycle Assessment of Electricity Generation from Low Temperature Waste Heat

‐‐‐ The Influence of Working Fluid

Lijun Bai

Master of Science in Industrial Ecology

Supervisor: Edgar Hertwich, EPT

Co‐supervisor: Thomas Gibon, EPT

External Contact: Yves Ladam, Sintef Energy

Submission Date: July 11, 2012

Norwegian University of Science and Technology Department of Energy and Process Engineering

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Acknowledgments

This thesis would not have been possible without the support of many

people. Many thanks to my supervisor Edgar Hertwich, Co‐supervisor

Thomas Gibon and external contact Yves Ladam for their academic and

technical guidance. Thanks to the Industrial Ecology Programme and

Sintef Energy for their generous support. And thanks to my family

members and classmates, their support is important for the completion

of this thesis.

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Abstract

With the increasing demand for clean energy to reduce the

consumption of fossil fuel and to limit the environmental burden, the

research towards the utilization of waste heat from various sources is

growing in recent years. In this thesis, environmental impacts of

electricity generation from low temperature waste heat using organic

Rankine cycle (ORC) power plants have been evaluated. Using the Life

Cycle Assessment (LCA) as the evaluation method, the environmental

impacts of NH3, R134a, CO2 and n‐Pentane as working fluids in ORC

power plants have been calculated. Comparing with wind power, the

results show that the overall environmental impacts from low

temperature waste heat ORC power plants are comparable with wind

power. And the working fluids have significant effects to the entire

environmental impacts of electricity production from ORC power

plants.

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Abstrakt

Wed den økende etterspørselen etter ren energi for å redusere

forbruket av fossilt brensel og for å begrense miljøbelastningen, er

forskningen mot utnyttelse av spillvarme fra ulike kilder økende de siste

årene. I denne oppgaven har miljøkonsekvenser av elektrisitet fra lav

temperatur spillvarme hjelp organic Rankine cycle (ORC) kraftverkene

blitt evaluert. Bruke livssyklusanalyser som metode for evaluering, de

miljømessige konsekvensene av NH3, R134a, CO2 og n‐pentan som

arbeider væsker i ORC kraftverk er beregnet. Sammenligning med

vindkraft, viser resultatene at de samlede miljøkonsekvensene fra

lavtemperatur spillvarme ORC kraftverk er kompatible med vindkraft.

Og arbeidsforholdene væsker ha betydelige effekter på hele

miljøkonsekvensene av strømproduksjon fra ORC kraftverk.

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Table of Contents

Acknowledgements……………………………………………………...2

Abstract……………………………………………………….................3

Abstrakt…………………………………………………………….........4

List of Tables…………………………………………………………..10

List of Figures………………………………………………………….11

Nomenclature…………………………………………………………..12

Chapter 1 Introduction…………………………………………………13

Chapter 2 Background and Literature Review…………………………17

2.1 Overview of Waste Heat Recovery……………………………..17

2.2 Organic Rankine Cycle as The Technology for Waste Heat

Recovery………………………………………………………..20

2.2.1 Thermodynamica Principle of Organic Rankine Cycle

and ORC Configuration…………………………………..22

2.2.2 Working Fluids in ORC Power Cycle…………………….26

2.2.3 Typical Working Fluids and Their Properties………….....30

2.3 CO2 as Working Fluid in Organic Rankine Cycle ……................30

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Chapter 3 Methodology ………………………………………………35

3.1 Introduction of Life Cycle Assessment………………………....35

3.1.1 Life Cycle Assessment ……………………………….......36

3.1.2 Life cycle inventory database…………………………….38

3.1.3 Basic mathematics of LCA……………………………….38

3.2 Life Cycle Impact Assessment……..............................................42

3.3 Calculation Method………………………………………….......43

3.3.1 Midpoint and endpoint approaches………………………...43

3.3.2 ReCiPe method…………………………………………….45

3.3.3 Software and method used in this research………………...49

Chapter 4 Life Cycle Analysis of NPO 210 kWe ORC Power Plant....51

4.1 Power Plant Description………………………………………..51

4.1.1 Configuration of the power plant………………………....51

4.1.2 Parameters in the power cycle……………………………52

4.1.3 Equipments used and the power plant layout……………53

4.2 Life Cycle Analysis of Power Plant……………………………55

4.2.1 Goal and scope……………………………………………55

4.2.2 Functional unit……………………………………………56

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4.2.3 Flowchart of NPO 210 kWe power plant………………..57

4.2.4 Data collection…………………………………………..57

4.2.5 Life cycle inventory of power plant……………………..58

4.3 Results and Discussion………………………………………….58

4.3.1 Overall characterization impacts from the 210 kWe ORC

power plant..........................................................................58

4.3.2 Percentage contribution of different life cycle stages.........60

4.3.3 Components percentage contribution for ORC assembly

in chosen categories............................................................60

4.3.4 Total impact amounts from the scenarios of four different

working fluids.....................................................................61

4.3.5 Results from the different working fluids...........................62

4.3.6 Discussion on the effect of working fluids ........................64

Chapter 5 Life Cycle Analysis of NPO 750 kWe ORC Power

Plant………………………………………………………...67

5.1 Power Plant Description………………………………………...67

5.1.1 Process scheme of the power plant……………………….68

5.1.2 Technical data of the 750 kWe power plant………………69

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5.1.3 Equipments used in this power plant……………………..69

5.2 Life Cycle Analysis of the Power Plant………………………...71

5.2.1 Goal and scope……………………………………………71

5.2.2 Functional unit……………………………………………72

5.2.3 Process flowchart of NPO 750 kWe power plant…………72

5.2.4 Data collection…………………………………………....73

5.2.5 Life cycle analysis inventory……………………………..73

5.3 Results and Discussion………………………………………....73

5.3.1 Total impact amounts of 750 kWe power plant…………...73

5.3.2 Life cycle stage contributions to the total amounts ……...74

5.3.3 Comparison between 210 kWe ORC power plant and

750 kWe power plant with NH3 as working fluid………...75

Chapter 6 The Environmental Impacts of ORC Power Plants

Comparing with Other Renewable Technologies …………...77

6.1 Comparison with Wind Power ………………………………...77

6.2 Comparison with Hydropower....................................................78

Chapter 7 Conclusion and Further Reconmmendation………………...79

Bibliography…………………………………………………………...80

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Appendix

Appendix I………………………………………………………….86

Appendix II…………………………………………………………88

Appendix III………………………………………………………...90

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List of Tables

Table 1: Properties of Typical ORC Working Fluids...............................30

Table 2: List of ReCiPe Midpoint Impact Categories……………………………48

Table 3: Total Characterization Impact Amounts of 210 kWe Power

Plant from Chosen Categories……………………….........................59

Table 4: Total Impact Amounts from Chosen Categories of 750 kWe

Power Plant from Four Working Fluids Scenarios…………………62

Table 5: Total Characterization Impact Amounts of 750 kWe Power

Plant from Chosen Categories.................................................73

Table 6: Comparison of Characterization Results from Two ORC Power

Plants.......................................................................................75

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List of Figures

Fig. 1: T ‐ S diagram of an Ideal Rankine Cycle………………………....23

Fig. 2: ORC Power Cycle Configuration………………………………...24

Fig. 3: Classification of the Working Fluids…………………………….29

Fig. 4: Configuration of CO2 Supercritical Power Cycle ………………32

Fig. 5: Illustration of LCA Phases……………………………………..37

Fig. 6: The Structure of Life Cycle Inventory Assessment……………...43

Fig. 7: Layout of NPO 210 kWe ORC Power Plant……………………..54

Fig. 8: Process Flowchart of NPO 210 kWe ORC Power Plant…………57

Fig. 9: Impacts from LCA stages of 210 kWe ORC Power Plant……..59

Fig. 10: Percentage Contribution from ORC Components……………60

Fig. 11: Total Impact Amounts of Chosen Categories……………...63-64

Fig. 12: Process Scheme of NH3 Power Plant………………………….68

Fig. 13: Images of Lysholm Turbine…………………………………...70

Fig. 14: Process Flowchart of 750 kWe Power Plant…………………..72

Fig. 15: Percentage Contributions from Life Cycle Stages of 750 kWe

ORC Power Plant.......................................................................74

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Nomenclature

ORC Organic Rankine Cycle

LCA Life Cycle Analysis

LCIA Life Cycle Inventory Analysis

WHR Waste Heat Recovery

NPO Net Power Output

WF Working Fluid

T Temperature

P Pressure

s Entropy

h Enthalpy

ηth ORC Thermal Efficiency

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Chapter 1

INTRODUCTION

With the increasing demand for clean energy to reduce the consumption of fossil

fuel and to limit the environmental load, while increasing the quality of life, the

research towards the utilization of waste heat from various sources is growing in

recent years. It is an interesting topic to do the research for evaluating the

environmental impacts of electricity generation from low temperature waste heat

concerning the influence of working fluids in the power plants.

In Norway, there are enormous waste energy sources from metallurgical industry,

refineries and process industries that produce exhaust heat which are currently

wasted. The researchers of Sintef Energy have been collaborating with other

international industry and research institutes ,working on improving energy

efficiency and developing cost-effective, environmentally- friendly waste heat

recovery and electricity generation technology based on the utilization of surplus

heat (Sintef Energy, 2011). One of the key points of this project is to identify the

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new energy technologies which can be applied to the related industries for

converting the waste heat into useful electricity from low-temperature sources.

In European industry, it is estimated that over 300 TWh of waste heat could be

available, which can be used either in district heating systems or for production of

electricity. Almost all production or consumption of energy loses large portion of

input energy. One example is in a standard combustion engine, for which only 35%

of the energy input is utilized, while the remaining 65% is lost as waste heat

(Öhman & Hedebäck, 2008). Finding ways to convert this enormous amount of

energy which are both thermodynamically efficient and technically practical is a

top priority.

In conventional thermal energy conversion in power plants, impacts connected to

constructing the power plant or manufacturing the equipment are not important for

the overall environmental impact of the electricity produced. A large portion of

the environmental impact is connected to the production of electricity. For the

developing of new technologies, given the energy source is waste heat, the

question is what are the environmental impacts caused by the equipment needed

for producing energy from the waste heat? What is the environmental benefit of

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using waste heat, compared other technologies for producing one unit of

electricity?

Much industrial waste heat is in the low-temperature range: around 60% of

unrecovered waste heat is low quality with the temperatures below 2320C (U.S.

Dep. of Energy, 2008). Based on the thermodynamic principle of Rankine cycle,

the low-temperature waste heat can actually be used for electricity generation.

Power plants based on the organic Rankine cycle (ORC) have been employed to

produce power from various heat sources; the size range of these power plants of a

few kilowatts to more than several megawatts have demonstrated the success of

this technology (Quoilin & Lemort, 2009).

With the increased demand for fossil fuels, the progress of clean energy

technologies research and their applications is making impressive pace in recent

years. For the application of new technologies, evaluating their overall

environmental impacts is necessary. LCA as one of the important environmental

tools has been applied to evaluate the environmental impacts of photovoltaic and

wind power (Jungbluth, Bauer, Dones, & Frischknecht, 2005), hydropower

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( Varun, Bhat, & Prakash, 2008), solar power ( Kannan, Leong, Osman, Ho,& Tso,

2006), etc.. For ORC power plant, there are no LCA researches that have been

performed. It should be a challenged topic to do for evaluating the environmental

impacts through the approach of LCA.

The environmental impacts of ORC power plants are closely related with the scale

of power plants, configuration of the ORC cycle, equipments chosen for those

power plants, and the working fluids. The choice of working fluids is important for

system performance, since they influence the system efficiency, operation, and

environmental impact (Liu, Chien, & Wang, 2004). The aim of this research is to

provide a life-cycle environmental impact evaluation of electricity from low-

temperature heat, comparing thermal cycles based on different working fluids

suitable for low-temperature heat sources.

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Chapter 2

BACKGROUND AND LITERATURE REVIEW

2.1 OVERVIEW OF WASTE HEAT RECOVERY

In general, industrial waste heat refers to energy that is generated from industrial

processes without being put into practical use. Various studies have estimated that

as much as 20% to 50 % of industrial energy consumption is ultimately discharged

as waste heat (U.S. Dep. of Energy). The main aim to seek and adopt alternate

renewable energy sources as well as converting technologies is to replace the

consumption of fossil fuels, which could get the environmental benefit through the

reduction of greenhouse gases and gain the economic benefit by using the power

produced from waste heat for district utility.

For waste heat recovery (WHR) , there are three necessary components: source of

waste heat, recovery technology and end use of the recovered energy. For utilizing

the waste heat source, both the quantity and quality (typically exhaust

temperatures) need to be considered. The technologies used should maximize the

heat recovery, expand application constrains and improve the economic benefit.

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Waste heat source temperatures have no standard classifications based on the

operation temperatures of power plants. In general, according to the temperature

ranges, the waste heat sources can be categorized as high temperature heat source;

medium temperature heat source; and low temperature heat source. U.S.

Department of Energy (2008) classified the temperature ranges as:

High Temperature: 6500C and higher

Medium Temperature: 2300C to 6500C

Low Temperature: 2300C and lower

The barriers for utilizing the vast amount of waste heat:

1). Cost: the cost concern rising from the long payback periods; material

constraints and costs; economics-of-scale; and operation and maintenance.

2). Temperature Restrictions: low-temperature power generation is currently in

development; material constraints and costs mechanical and chemical properties in

high temperature and corrosion of materials in low temperature.

3). Chemical Composition: temperature restrictions; heat transfer rates;

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material constraints and costs; operation and maintenance costs; environmental

concerns and product/process control.

4). Application-specific Constraints: equipment designs must be adapted to the

needs of a given process; heat recovery can complicate process control systems.

5). Limited Space and Inaccessibility.

Waste heat temperature is a key factor for the adaption of technologies in the waste

heat recovery power plants. The theoretical (Carnot) efficiency is limited when the

temperature of heat source is low, and the net work is proportional to the source

temperature drop between the heat source and heat sink (Nekså & Ladam, 2009).

Based on the Carnot efficiency, the maximum efficiency at given heat source and

heat sink is defined as:

ηth = 1 – TL/TH

TH is the waste heat temperature, TL is the heat sink temperature.

The efficiency ηth is higher at the higher heat source temperature and the efficiency

ηth is lower at the lower heat source temperature.

Mostly depending on the temperature, the technologies for WHR include:

1). Steam Power Cycle

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Steam power plant which uses the waste heat to produce steam and then drives a

steam turbine for producing output work is the most frequently

used power cycle. Historically, steam power plants have been used for medium to

high temperature waste heat recovery.

2). Organic Rankine Cycle

At lower temperature, instead of steam power cycle, organic Rankine cycle with

organic substances as working fluids has been employed, since at the low-

temperature waste heat may not provide sufficient superheating for the running of

turbine.

3). Other Technologies

CO2 transcritical power cycle with CO2 as working fluid has getting increased

attention for the conversion of low-temperature waste heat and recently developed

Kalina cycle is a suitable technology for the low – to medium-temperature waste

heat sources.

2.2 ORGANIC RANKINE CYCLE AS THE TECHNOLOGY FOR WASTE HEAT RECOVERY

ORC is an environmentally friendly technology with no emissions such as CO,

CO2, NOx, SOx and other atmospheric pollutants to the environment. The most

important advantage for ORC as one of the renewable energy technologies is that

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ORC can be used in various kinds of low-grade heat sources for power generation

including industrial waste heat recovery from industrial waste heat streams,

biomass, geothermal, and solar energy.

ORC in Industrial waste heat recovery:

Gas compressor stations: recover energy from pipeline compressor stations.

Gas processing plants: transfer waste heat from gas turbine exhaust.

Power generation: heat recovery on internal combustion engines.

Steel and aluminum industries: utilize the vast amount of waste heat from

steel and aluminum refineries.

Other industrial processes: pulp and paper mills; chemical plants; cement

factories; glass plants; etc.

ORC in other areas:

Biomass application represents important portion of ORC applications ---

around 48% of market share of ORC is from Biomass (Quoilin & Lemort,

2009).

There is significant geothermal market potential in the EU and in global

regions, which could be used for electricity generation based on ORC

technology.

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ORC technology also can be used to generate electricity from solar

energy transferred from solar collectors --- an alternative to photovoltaic

cells and solar plants.

2.2.1 Thermodynamic Principle of Organic Rankine Cycle and ORC

Configuration

Based on Rankine cycle, organic Rankine cycle (ORC) uses organic substances as

working fluids to recover heat from low temperature heat sources. The

thermodynamic principle of Rankine cycle is the first law of thermodynamics,

which states that the output work can be produced by expanding working fluids

from high pressure state to low pressure state.

An ideal Rankine cycle includes four processes [Fig. 1]:

A. Heat transferred from waste heat source to working fluid, the working fluid

phase is changed from liquid to gas (2-2’-3).

B. High temperature and pressure gas expanded and the output work

produced(3-4);

C. Working fluid condensed in the constant pressure(4-1);

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D. Liquid working fluid compressed by the pump to form high pressure liquid

(1-2).

Fig. 1: T - S Diagram of an Ideal Rankine Cycle

A basic organic Rankine cycle consists of four main components: evaporator,

condenser, turbine, and working fluid pump.

T

sa b c

1

2

2’’ 3

3’

4 4’

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In the evaporator and preheater, the heat is transferred to the working fluid from

the heat source, liquid working fluid is heated and evaporated; output work is

produced in turbine and the synchronous generator; steam from the outlet of

turbine is condensed in the condenser by the cold source, which could be the local

lake water or other cold water; and the working fluid pump to raise the pressure of

liquid working fluid to the required operation pressure.

A typical ORC power cycle has been demonstrated in Fig. 2:

Fig. 2: ORC Power Cycle Configuration

Heat

Source Evaporator

Turbine &

GeneratorElectricity

Cold

Source Condenser

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Other configurations such as regenerative ORC power cycles with internal heat

exchanger and the ORC power cycle with superheating are frequently used in ORC

power plants (Mago, P. J., Chama, L. M., Srinivasan, K., & Somayaji, C., 2008);

(Roy & Mstra, 2012); and (Roy, Mishra & Misra, 2011).

The efficiency of ORC for converting heat to work can be expressed as:

ηth = (Wt – Wp) / Qin * 100

Wt: turbine output work

Wp: work consumed by the pump

Qin: heat transferred from heat source

The efficiency of ORC is related with the configuration of power cycle, operation

pressure, temperature of heat source and heat sink, working fluid properties,

efficiency of turbine and pump, etc.. Wei et al. (2007) in their paper Performance

analysis and optimization of organic Rankine cycle for waste heat recovery

analyzed the thermodynamic performances of an ORC system using R245fa as

working fluid. They concluded that maximizing the usage of exhaust heat as much

as possible and the higher grade of heat source can improve system output net

power and efficiency and the condenser should be cooled properly to reach the

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peak system efficiency (Wei, Lu, Lu, & Gu, 2007). The research from Roy et

al.(2011) revealed that non-regenerative ORC during superheating using R123

produces the maximum efficiencies and turbine work output for constant as well as

variable heat source temperature conditions among four working fluids R12, R123,

R-134a and R717 (Roy, 2011). Kuo, Chang, & Wang (2011) analyzed a 50 kW

organic Rankine cycle system for the effect of heat exchangers. The results

indicate that the dominant thermal resistance in the shell-and-tube condenser is on

the shell side and the dominant thermal resistance is on the refrigerant side for the

plate evaporator (Kuo, 2011). And Yamamoto, Furuhat, Arai, & Nori (2001) in

their paper “ design and testing of a organic Rankine cycle” did the research for the

optimal operation conditions of ORC theoretically and experimentally. They found

that there are optimum operating conditions between the rotation speed and the

turbine outlet and R-123 improves the cycle performance in the large extent

comparing with traditional working fluid water (Yamamoto, 2001).

2.2.2 Working Fluids in ORC Power Cycle

Considering the environmental impacts of ORC power plants, one of the

disadvantages is the working fluid. Traditional organic working fluids used in

ORC such as silicone oil, R245fa and R134a suffer from being excessively priced

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as well as suffering environmental drawbacks. Researchers are investigating the

use of naturally occurring substances such as hydrocarbons, NH3 and CO2.

In general, good working fluids should satisfy the following criteria:

High thermal efficiency for the given heat source and heat sink

temperatures;

Low specific volumes;

Moderate pressure in the heat exchangers;

Low liquid viscosity and high liquid thermal conductivity;

High latent heat of vaporization;

Low toxicity; No –flammable and non-corrosive;

Low ODP and low GWP;

Low cost and good availability;

The selection for working fluids varies with types of ORC power plants,

manufacturers, heat sources, availability, etc.. Except the direct environmental

impacts, working fluids also have significant influence to the environmental

impacts considering the thermal efficiency of ORC power plant. With higher

efficiency, the consumption of working fluid could be lower, and areas required for

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the heat exchangers could be lower, both factors contribute lower

environmental impacts from the life cycle assessment point of view.

ORC manufacturer Ormat uses n-pentane as the working fluid for heat source

temperature range of 1500C – 3000C, and the output power range is from 200 kWe

to 72 MWe. ORC manufacturer Turboden used OMTS as the main working fluid

with the temperature range of 1000C – 3000C, and the output power range is 200

KWe to 2 MWe. The working fluids of other manufacturers include hydrocarbons,

R245fa, R134a, etc.(Quoilin & Lemort, 2009).

The working fluid can be classified on three categories of working fluids: dry,

isentropic and wet depending on the slope of the T –S diagram of working fluids

[Fig. 3].

An isentropic fluid has nearly infinitely large slopes, examples are R11, R12,

R134a --- illustrated in diagram (a); a wet fluid has negative slope, examples are

water and ammonia --- illustrated in diagram (b). Wet types of working fluids often

have low molecular weight; a dry fluid has positive slopes, examples for dry fluids

are benzene, R113, R245fa, R123, isobutane --- illustrated in diagram (c).

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Dry and isentropic fluids have better thermal efficiencies considering the droplet in

turbine. Isentropic fluids are most suitable for recovering low-temperature waste

heat with the property of vapor saturated at the turbine inlet will remain saturated

throughout the turbine exhaust without condensation, so the regenerator is not

necessary. Research also indicates that dry fluids can reach efficiencies if a

regenerator is added to the cycle (Saleh, Koglbauer, Wendland, & Fischer, 2007).

Fig. 3: Classification of Working Fluids (Mego et al, 2008)

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2.2.3 Working fluids and their properties

Table 1: Properties of typical ORC working fluids

Parameters R‐12 R‐123 R134a R717 R747

Chemical formulae CF2Cl2 CF3CHCl2 CF3CH2F NH3 CO2

Molecular weight(g/mol) 120.92 152.93 102.03 17.031 44.01

Boiling point(0C) ‐29.8 27.85 ‐26.15 ‐33.35 ‐57

Critical Temperature(0C) 112.04 183.79 101.06 133.0 33.1

Critical pressure(bar) 41.15 36.74 40.56 112.97 73.8

Atmospheric lifetime(yrs) 100 1.40 52.0 ‐‐‐ N/A

Ozone depletion potential 0.82 0.012 0.00 ‐‐‐ 0

Global warming potential

(at 100 years) 1060 120.0 1300.0 0 1

Source: (Roy, Mishra & Misra, 2011)

2.3 CO2 AS WORKING FLUID IN ORGANIC RANKINE CYCLE

With the non-toxic and non-combustible natural properties, and inexpensive cost of

CO2, as well as non-explosive and abundance in the nature, CO2 as a working fluid

is getting increased attention in the industrial applications.

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CO2 has following special properties as working fluid in ORC:

1). Low critical temperature is suitable for the low temperature heat source.

2). Ozone depletion potential (ODP) is zero and global warming potential (GWP)

100 years is 1.

3). Abundant, non-flammable, non-toxic and low cost.

4). Favorable thermodynamics and transports properties.

The basic principle of CO2 power plant is still the Rankine cycle. The CO2 power

cycle includes four principle processes: compression, heat transferred from heat

sources, expansion and condensation and at least five components: evaporator,

condenser, turbine, pump and working fluid. Since CO2 has a low critical

temperature of CO2, the CO2 power cycle is a transcritical cycle: Part of the cycle

is located in the supercritical region which could affect the configuration of CO2

power cycle (Cayer, Galanis, & Nesreddine, 2010). The configuration of CO2

power cycle includes regenerator (or internal heat exchanger) because of its special

supercritical property [Fig. 4 ].

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Fig. 4: Configuration of CO2 Supercritical Power Cycle (Chen at el , 2010)

CO2 as a promising working fluid of ORC is getting more and more attention.

Chen, Lundqvist, Johansson, & Platell (2006 ) carried on the research for the

comparison of CO2 transcritical power cycle with ordinary organic working fluid

R123 in waste heat recovery. The results show that with the same temperature of

heat source, the CO2 transcritical power system gives a slightly higher power

output than R123 as working fluid. Further, the power system with carbon dioxide

as a working fluid is also more compact and more environmental friendly than the

one with organic working fluid. Cayer et al (2010) analyzed a CO2 transcritical

power cycle for an industrial low-grade stream of process gases as its heat source.

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By varying the high pressure of the cycle and its net power output with fixed

temperatures and mass flow rates of the heat sources, he concluded that the

existence of optimum high pressure of the cycle. Andresen, Ladam, & Nekså,

(2011) investigated the simulation optimization of the power cycle and heat

exchanger parameters, this methodology can be adapted to analyze and compare

cycles of different complexity, working fluids and boundary conditions. Ladam &

Skaugen(2007) in their technical report “CO2 as working fluid in a Rankine cycle

for electricity production from waste heat sources on fishing boats” showed that

performances for low temperature waste heat are significantly improved(25%) with

a CO2 technology. Energy (fuel) savings up to 10% can be achieved.

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Chapter 3

METHODOLOGY

In this paper, Life Cycle Assessment methodology is used to evaluate the

environmental impacts for producing electricity from low temperature waste heat

sources in the situations of different working fluids.

3.1 INTRODUCTION OF LIFE CYCLE ASSESSMENT

A life-cycle Assessment(LCA) method systematically assesses and evaluates

environmental aspects associated with all the stages of a product’s life from raw

material acquisition to final disposal (from “cradle to grave”). Life cycle

assessment can be used in a wide range of products and activities, from agriculture

to energy system, from packaging products to transportation vehicles, and which

could integrated into strategic levels of firms and corporate, and further for the

reference of different decision makers.

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3.1.1. Life cycle assessment

Traditionally, the LCA method consists of four main steps [Fig. 5]:

Goal and scope definition; Inventory analysis; Impact assessment; and

Interpretation.

Step 1). Goal and scope definition:

The purpose of the LCA analysis is decided. The goal definition includes stating

the intended application of the study, the reason for carrying it out and to whom

the results are intended to be presented. In the phase of goal and scope definition,

the functional unit and system boundary are defined. Inventory analysis is to build

a systems model according to the requirements of a goal and scope definition.

Step 2). Inventory analysis:

1). Construction of the flow model: the flow model is usually a flowchart which

shows the activities within the analyzed system and the flows between those

activities.

2). Data Collection for all those activities such as raw materials, energy

consumption, products, and waste and emissions to air and water.

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3). Calculation of the amount of resource use and pollutants of the system with

related to the functional unit.

Life Cycle Assessment Framework

Fig. 5: Illustration of LCA Phases (ISO 2006a)

Step 3). Impact assessment or Life Cycle Assessment (LCIA): the procedure to

quantify the environmental impacts loads in the inventory analysis.

Step 4). Interpretation: the process of refining the raw results into useful,

presentable and final results. Most often method is to present only the most

Goal and Scope Definition

Inventory

Analysis

Impact

Assessment

Interpre

tation

Direct applications:

‐‐Product

development and

improvement

‐‐Strategic planning

‐‐Public policy

making

‐‐Marketing

‐‐Other

38 | P a g e

important inventory result parameters in a bar diagram and weighted impact

assessment results.

3.1.2 Life cycle inventory database

Publicly available high quality life cycle inventory (LCI) databases have been

known as Franklin US98, Idemat 2005, Buwal 250, ETH-ESU 96, and Ecoinvent.

Among them, Ecoinvent database developed by the Ecoinvent Center has been

recognized as the most recent, comprehensive and best quality LCA database

available. The first launch of Ecoinvent data v1.01 was in 2003, and the latest

version is Ecoinvent v.2.2 leased in 2009. The version used in this research for life

cycle inventory assessment(LCIA) is Ecoinvent v2.1, which includes about 4000

datasets for products, services, and processes often used in LCA case

studies(Ecoinvent, 2007) , covering energy, transport, building materials,

chemicals, mechanicals, electronics, waste treatment and agricultural products.

3.1.3 Basic mathematics of LCA

Considering LCA is the calculation of emissions from the entire production value

chain, the total emissions include direct emission from the production and service

and the indirect emissions from related production and service activities.

39 | P a g e

1) Production output equation

x = A *x + y

x : output

x1

x = x2

…

xn

A: intermediate demand matrix

a11 a12 … a1n

A= a21 a22 … a2n

…..

an1 an2… ann

y: external demand

y1

y = y2

…

yn

40 | P a g e

2) Leontief inverse matrix

x = ( I –A ) -1 y ↔ x =L y

I : unit matrix

L = ( I-A)-1: Leontief inverse matrix

1-a11 –a12 … -a1n -1 l11 l12 … l1n

L = -a21 1-a22 … -a23 = l21 l22 … l2n

…. …..

-an1 –an2…. 1-ann ln1 ln2 … lnn

3) Calculation of total emissions for a given external demand

e = S* x = S * L *y

S: stressor intensity matrix

s11 s12 … s1, pro

S = s21 s22 … s2, pro

….

sstr,1 sstr,2… sstr, pro

41 | P a g e

e: vector of stressors generated for a given external demand

e1 e = e2 … estr

4). Impact evaluation of different categories

d = C*e = C*S*(I-A)-1*y

C: Characterization factor matrix

c11 c12 … c1,str C = … … … … cimp,1 cimp,2… cimp,str

d1

d = .

.

dimp

42 | P a g e

LCIA interpretation calculation:

1. Characterization

d = C*e

d = category indicator vector(potentials)

C = characterization factor matrix

e = LCI vector

2. Normalization

n = N* d

n = normalized category indicator vector

N = normalization matrix

3. Weighting

t = w*n

t = single aggregated indicator

w = vector of weighting factors

3.2 LIFE CYCLE INVENTORY ASSESSMENT

From the life cycle inventory data, the steps for evaluating the environmental

impacts are illustrated in [Fig. 6]:

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1). Classification:

Assigning the inventory items to different environmental impact

categories.

2). Characterization:

Multiplying the inventory items by characterization factors to obtain

the category indicator values.

3). Normalization (optional)

Expressing the required category indicators as the portion of given

type of total impact.

4). Weighting (optional)

Multiplying the category factors to get the social importance of

responding categories.

3.3 CALCULATION METHODS

3.3.1 Midpoint and endpoint approaches

Generally, there are two calculation methods: midpoint methods and endpoint

methods. In the midpoint approach, environmental impacts from products or

processes are related to damage categories such as climate change, ecotoxicity

acidification. In endpoint approach, the final social and health consequences such

44 | P a g e

Fig. 6: The Structure of Life Cycle Inventory Assessment

as damage to human health and damage to ecosystem quality are obtained based on

a common attribute ($ or DALY).

Midpoint methods

CML-method

EDIP 2003

Impact 2000 (CMIL2)

Inventory

Classification

Characterization

Valuation

45 | P a g e

TRACI

Endpoint methods:

Ecoindicator 99

Environmental Priority System

Ecoscarcity method

3.3.2 ReCiPe method

Newly developed ReCiPe comprises of two sets of impact categories: midpoint

level and endpoint level.

There are eighteen impact categories at the midpoint level of ReCiPe. Ten of them

have been chosen for reporting (ReCiPe 2008, 2009):

1. Climate Change

Characterization factor is Global Warming Potential (GWP), the environmental

impact effect is the amount of kg CO2 equivalent to air.

2. Ozone Depletion

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Characterization factor is Ozone Depletion Potential (ODP), the environmental

impact effect is the amount of kg CFC-11 equivalent to air.

3. Terrestrial Acidification

Characterization factor is Terrestrial Acidification Potential (TA), the

environmental impact effect is the amount of kg SO2 equivalent to air.

4. Freshwater Eutrophication

Characterization factor is Freshwater Eutrophication Potential (FE),

the environmental impact effect is the amount of kg P equivalent to freshwater.

5. Marine Eutrophication

Characterization factor is Marine Eutrophication Potential(FE), the

environmental impact effect is the amount of kg N equivalent to

freshwater.

6. Human Toxicity

Characterization factor is Human Toxicity Potential (HT), the

environmental impact effect is the amount of kg 1,4-DCB equivalent

to urban air.

7. Photochemical Oxidant Formation

Characterization factor is Phtochemical Oxidant Formation Potential (POF), the

environmental impact effect is the amount of kg NMVOC to air.

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8. Particulate matter formation

Characterization factor is Particulate Matter Formation Potential (PMF), the

environmental impacts effect is PM10 equivalent to air.

9. Terrestrial Ecotoxicity

Chracterization factor is Terrestrial Ecotoxicity Potential (TET), the

environmental impacts effect is kg 1,4-DCB equivalent to industrial soil.

10. Freshwater Ecotoxicity

Charaterization factor is Freshwater Ecotoxicity Potential (FET), the

environmental impacts effect is kg 1,4 –DCB to freshwater.

And other categories:

11. Marine Ecotoxicity

12. Ionizing Radiation

13. Agricultural Land Occupation

14. Urban Land Occupation

15. Natural Land Transformation

16. Water Depletion

17. Mineral Resource Depletion

18. Fossil Fuel Depletion

48 | P a g e

And three endpoint categories at the endpoint level of ReCiPe method:

1. Damage to human health

Indicator is Disability-adjusted Loss of Life Years (DALY) in

years (yr).

2. Damage to ecosystem diversity

Indicator is Loss of Species during a year in years (yr).

3. Damage to resource availability

Indicator is Increased Cost in dollars ($)

Table 2: List of ReCiPe Midpoint Impact Categories

Source: ReCipe 2008 (2009)

49 | P a g e

There are three perspectives are concerned in ReCiPe:

Individualist perspective (I): technology optimist based on short-term

interest. The individualist perspective assumes a short time frame of 20 year

time frame.

Hierarchist perspective (H): problem solver based on the most common

policy principles. The hierarchist perspective seeks consensus for the 100

year timeframe.

Egalitarian perspective (E): extreme sustainability considering the longest

time-frame, assuming 500 years. For the substances with short lifetime, the

results will be the same.

3.3.3 Software and method used in this research

In this research, software used for LCA assessment is SimaPro 7.3.2 from Pré

Consultants, Neitherland and the method used here is the ReCiPe midpoint

method, Hierarchist version(European normalization) created by RIVM, CML,

Pre Consultants, Radboud Universitert Nijmegen and CE Delft(SimaPro 7.3.2).

50 | P a g e

51 | P a g e

Chapter 4

LIFE CYCLE ANLAYSIS OF NPO 210 kWe ORC POWER PLANT

4.1 POWER PLANT DESCRIPTION

The power plant used for LCA analysis is the Geothermal Power Plant at Chena

Hot Springs, Alaska with the power capacity of 210 kWe NPO. The higher

temperature heat source is the hot water from local geothermal hot spring and the

low temperature heat sink is the local river water. The purpose of this project is to

generate electricity from the available geothermal resource for local power supply,

usually this power is generated by diesel generation sets. Manufactured by

Turboden, this power plant is a successful application case for the R134a as

working fluid in organic Rankine cycle. The model used in Chena project is the

same as the Turboden PureCycle 280 model, which has been installed for

electricity generation from waste heat recovery in various situations (Turboden,

2012)

52 | P a g e

4.1.1 Configuration of the power plant

The power plant produces electricity using ORC power cycle with

R134a as working fluid. For the LCA, other working fluids Ammonia, CO2 and

Pentane have been included. Same as other ORC power plants, this power plant

consists of evaporator and preheater set, turbogenerator, condenser, working fluid

pump and working fluid itself.

In evaporator and preheater set, heat is transferred from waste heat source to

working fluid for evaporating, the liquid working fluid becomes higher pressure

vapour to enter into the inlet of turbine. In turbogenerator, this higher pressure

vapour is expanded to generate electricity. In condenser, the working fluid from

the outlet of turbine is condensed into liquid. Then the liquid working fluid is

pressured in the working fluid pump and then enters into the evaporator to

complete the power cycle.

4.1.2 Parameters in the power cycle

In this power plant, the gross output power of turbine is 250 kW and the net power

produced is 210 kW. In the evaporator/preheater side of the ORC system, the flow

rate of 33,44 l/s hot water enters the unit at the temperature of 850C and leaves at

the temperature of 70 0C, transferring 2,58 MW of themal energy to the working

53 | P a g e

fluid. In condenser, 50C of cooling water is heated to 100C transferring 2,36 MW

energy from the working fluid. In pump, the working fluid pressure is raised from

4 bar to 15 bar. The efficiency of this power plant is 8.2%. With the same heat

source and heat sink temperature, a completely reversible

thermodynamic cycle would have a thermal efficiency nearly 18%. Efficiency

improvement in this power plant is not critical from the economic point of view

since the heat source and then the fuel is essentially free.

4.1.3 Equipments used and the power plant layout

The sizes of this power plant unit are roughly estimated, around 5.1 meters length

and 1.75 meter height. The basic layout of this power plant is illustrated in Fig. 7

below:

Equipments:

Evaporator/Preheater:

Evaporator is the type of shell-and-tube heat exchanger which integrated

evaporator and preheater into one unit. The material used in this unit is Cupro-

Nickel 90-10. In boiler region, there are 1-pass 260 tubes; in preheater region,

there are 1-pass 90 tubes.

54 | P a g e

Condenser:

Condenser is a standard two pass shell-and-tube heat exchanger. There are 602 fin

types tubes and the material used is copper.

Fig. 7: Layout of NPO 210 kWe ORC Power Plant (LLC, 2007)

Turbogenerator:

Manufactured by United Technology Corporation, the turbogenerator combines a

radial inflow turbine with an internal gearbox and an induction generator in a

55 | P a g e

single hermetically sealed unit. Generator cooling is provided by the working fluid

and the turbine is internally lubricated by high temperature lubricant which is

compatible with the working fluid.

Working Fluid Pump:

The pump used in this power cycle is a regenerative pump manufactured by Roth

Pump Company.

Working Fluid: the built-in working fluid of this power plant is R134a. R134a is

frequently used in ORC power plant. With the chemical formula of CH2FCF3, the

molecular weight of R134a is 102,03 kg/kmol and the boiling point of R134a is -

26,15 at atmosphere pressure. Following the initial charge of liquid R134a in the

assembling stage of power plant, the working fluid is also supplied considering the

leakage in the maintenance and repair.

Other three potential working fluids for LCA analysis are NH3, CO2 and n-Pentane.

NH3 and CO2 are well-known substances in the nature. For the n-Pentane, the

critical temperature of n-Pentane is 96,68 oC, critical pressure is 42,47 bar.

4.2 LIFE CYCLE ANALYSIS OF THE POWER PLANT

4.2.1 Goal and scope

56 | P a g e

The goal of this study is to evaluate the environmental impacts associated with the

production of 210 kWe NPO electricity for the ORC power plant with organic

R134a as working fluid. The sizes of the power plant are relatively small, but

considering the increased demand for the fossil fuel energy, it is necessary to pay

attention for the small scale power plants. The LCA evaluation of this ORC power

plant will give the quantitative amounts of environmental impacts considering the

effects to human health, ecosystem health, and the damage to nature resources.

Through the performance of Life Cycle Analysis, the environmental impacts of

electricity production from ORC power plants have been determined, which have

been the basic data for comparing with other renewable energy technologies. Also

the environmental impacts of other potential working fluids NH3 and CO2 for ORC

power plants have been performed by the LCA.

4.2.2 Functional unit

The functional unit of this analysis is 1 kWh electricity generated from this R134a

power plant. This is based on the lifetime of 25 years and accounting for all the

mechanical and electrical losses for operating this power plant.

4.2.3 Flowchart of NPO 210 kWe power plant

The process flowchart of this power plant has been illustrated in Fig. 8 below:

57 | P a g e

Fig. 8: Process Flowchart of NPO 210 kWe Power Plant

4.2.4 Data collection

The principal manufacturing data of equipments have come from the a project

description of 400kW Geothermal Power Plant at Chena Hot Springs(LLC, 2007),

the information of given manufacturers, and from the SimaPro database.

Turbine/

Generator

Condenser

Evaporator/

Preheater

Working Fluid

Pump

R134a

Operation/

Maintenance

ORC Assembly

End‐of‐Life

Treatment

Raw

Material

Raw

Material

Raw

Material

ORC Power

Plant

1 kWh

58 | P a g e

4.2.5 Life cycle inventory of the power plant

The Life Cycle Inventory include the raw materials extraction and production,

energy consumption, transport, assembly of ORC components, construction of

ORC power plant, operation and routine maintenance, and disposal. For the

assembly, included for process inputs are evaporator/preheater; condenser;

turbine/generator; pump; and the assmbly of all those components and the entire

assemly of ORC power plant; For operation and maintenance; included are all the

operation and maintenance of all above equipments and the raw materials inputs;

For disposal, included are all the solid and liquid end-of - treatment considering

their environmental effects.

4.3 RESULTS AND DISCUSSION

4.3.1 Overall characterization impacts from the ORC power plant

The total characterization impact amounts of chosen categories have been

calculated which include all the life cycle stages of this ORC power plant: ORC

and components assembly, plant construction, operation and maintenance, and

end-of-life treatment. Results have been listed on Table 3.

59 | P a g e

Typically, for producing 1 kWh electricity from the ORC power plant of 210 kWe

using R134a as working fluid, the impact amount for climate change is 9,253 g

CO2 eq; for ozone depletion is 0,0007817 g CFC-11 eq; amount for human toxicity

is 2,686 g 1,4-DCB eq; etc..

Table 3: Total Impacts of 210 kWe ORC Power Plant from Chosen Categories

Impact categories Unit Total Amount

Climate Change kg CO2 eq 0,009253

Ozone Depletion kg CFC‐11 eq 7,817E‐7

Human Toxicity kg 1,4‐DCB eq 0,002686

Photochemical Oxidant Formation kg NMVOC 8,914E‐6

Particulate Matter Formation kg PM10 eq 8,993E‐6

Ionising Radiation kg U235 eq 0,000585

Terrestrial Acidification kg SO2 eq 2,64E‐5

Freshwater Eutrophication kg P eq 1,801E‐6

Marine Eutrophication kg N eq 5,856E‐6

Terrestrial Ecotoxicity kg 1,4‐DCB eq 3,498E‐7

4.3.2 Percentage contribution of different life cycle stages

In the life cycle analysis stage, the environmental impacts from assembly,

operation, setup construction and disposal have been calculated. Fig. 9 below

60 | P a g e

shows the percentage distribution from those stages.

Fig. 9: Percentage Contribution of Different Life Cycle Stages

4.3.3 Components percentage contribution for ORC assembly in chosen

categories

Fig. 10 below illustrates the percentage contribution from the main components of

ORC power plant for the chosen categories. For climate change and ozone

depletion, the most important contribution comes from the working fluid R134a;

for other categories, power output device turbine and generator has significant

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

CC(kg CO2 eq) 0,009253

OD(kg CFC‐11 eq) 7,817E‐7

HT(kg 1,4‐DCB eq) 0,002686

POF(kg NMVOC) 8,914E‐6

PMF(kg PM10 eq) 8,993E‐6

IR(kg U235 eq) 5,85E‐4

TA(kg SO2 eq) 2,64E‐5

FE(kg P eq) 1,801E‐6

ME(kg Neq) 5,856E‐7

TET(kg 1,4‐DCB eq) 3,498E‐7

Assembly Operation Construction/Disposal

contribu

contribu

Fig. 10:

4.3.4 T

fl

The tota

have be

CC

OD(kg

HT(kg

POF(

PMF(k

IR(k

TA

M

TET(kg

ution to the

ution to the

: Percentag

Total impa

uids

al impact a

een listed o

0%

C(kg CO2 eq)

g CFC‐11 eq)

1,4‐DCB eq)

kg NMVOC)

kg PM10 eq)

kg U235 eq)

A(kg SO2 eq)

FE(kg P eq)

ME(kg N eq)

1,4‐DCB eq)

Evaporato

e total amo

e total amo

ge Contrib

ct amount

amounts fro

on the table

%

or/Preheater

ounts; and

ounts.

bution of O

ts from the

om chosen

e below [T

20%

Condenser

heat excha

ORC Comp

e scenario

n categorie

able 4]:

40%

r Pump

angers have

ponents

os of four d

s for the di

60%

Turbine/Ge

e large por

different w

ifferent wo

80%

nerator W

61 | P

rtion of

working

orking fluid

% 10

WF/R134a

a g e

ds

00%

62 | P a g e

Table 4: Total Impact Amounts from Chosen Categories of 750 kWe Power

Plant from Four Working Fluids Scenarios

R134a Ammonia CO2 Pentane

Climate change(kg CO2 eq) 0.009253 0.0006764 0.002639 0.0012785

Ozone depletion(kg CFC-11 eq) 7.82E-07 5.26E-11 1.85E-10 8.41E-11

Human toxicity(kg 1,4-DCB eq) 0.002686 0.0009877 0.004109 0.0019423Photochemical oxidant formation(kg NMVOC) 8.91E-06 2.50E-06 1.06E-05 5.09E-06

Particulate matter formation(kg PM10 eq) 8.99E-06 2.79E-06 1.17E-05 5.48E-06

Ionising radiation(kg U235 eq) 0.000585 0.000182 0.0007903 3.68E-04

Terrestrial acidification(kg SO2 eq) 2.64E-05 7.61E-06 3.36E-05 1.51E-05

Freshwater eutrophication(kg P eq) 1.80E-06 6.56E-07 2.77E-06 1.29E-06

Marine eutrophication(kg N eq) 5.86E-07 1.73E-07 1.85E-10 3.36E-07

Terrestrial ecotoxicity(kg 1,4-DCB eq) 3.50E-07 1.38E-07 5.66E-07 2.50E-07

4.3.5 Results from the different working fluids

With the different physical and thermodynamic properties, the results of

environmental impacts are different for the working fluids. Fig. 11

below shows the environmental impacts comparison for the scenarios of all the

four working fluids: R134a, Ammonia, CO2 and n-Pentane. Fig. 11(a )includes the

categories of climate change, human toxicity and ionizing radiation; Fig. 11(b)

includes the categories of ozone depletion, marine eutrophication and terrestrial

ecotoxicity; Fig. 11(c )include all other four categories: photochemical oxidant

63 | P a g e

formation, particulate matter formation, terrestrial acidification and freshwater

eutrophication.

Fig. 11(a): Comparison of Working Fluids Effect

Fig. 11(b): Comparison of Working Fluids Effect

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.01

Climate change(kg CO2 eq)

Human toxicity(kg 1,4‐DB eq)

Ionising radiation(kg U235 eq)

R134a

Ammonia

CO2

Pentane

0.00E+001.00E‐072.00E‐073.00E‐074.00E‐075.00E‐076.00E‐077.00E‐078.00E‐079.00E‐07

R134a

Ammonia

CO2

Pentane

64 | P a g e

Fig. 11(c): Comparison of Working Fluids Effect

4.3.6 Discussion on the effect of working fluids

Climate change has harmful effect on a number of environmental mechanisms on

human health and ecosystem health. With the characterization factor of CO2

equivalency, R134a has quite larger CO2 equivalent amount over other three

working fluids, the relative scale comparing with NH3 is about 10 times higher and

several times over CO2 and n-Pentane.

Ozone Depletion

0.00E+00

5.00E‐06

1.00E‐05

1.50E‐05

2.00E‐05

2.50E‐05

3.00E‐05

3.50E‐05

4.00E‐05

R134a

Ammonia

CO2

Pentane

65 | P a g e

Ozone is formed by the action of sunlight and chemical reactions in the

stratosphere, and the stratospheric ozone is vital for life because it hinders solar

ultraviolet UV-B radiation. R134a has overcoming amount of ozone depletion

potential over other three working fluids represented by CFC-11 equivalent.

Eutrophication

Aquatic eutrophication is caused by the nutrient enrichment of the aquatic

environment. Eutrophication leads to environmental problems which affect the

speices diversity at varying levels. R134a has dominant emission amount of N in

the category of marine eutrophication and CO2 has highest score for P in the

category of freshwater eutrophication.

Acidification

CO2 has the highest impact on the acidification among these four working fluids.

Toxicity

The human toxicity and ecotoxicity account for the fate (environmental

persistence), exposure, and toxicity effect of a chemical. CO2 as working fluid has

highest amount of 1,4-DCB both on human toxicity and terrestrial ecotoxity.

66 | P a g e

67 | P a g e

Chapter 5

LIFE CYCLE ANALYSIS OF NPO 750 kWe ORC POWER PLANT

5.1 POWER PLANT DESCRIPTION

The power plant used in this research for LCA analysis is the ORC power plant

with NH3 as working fluid. The heat source of this ORC power plant comes from a

paper mill located at Aspa, Sweden, which produces bleached and unbleached pulp

at a capacity of 200,000 tons/year (Öhman, 2012). The waste heat comes from

several parts of the manufacturing processes and the cooling source is local lake

water. With the output power of 750 kWe, this ORC power plant could supply at

least 3133 MWh/year electricity to the local utility (Öhman, 2012). Without the

installation of the ORC power plant, all of the mill’s process water reaches the

local lake. With the installation of ORC power plant, the waste heat water is

transformed into emission free electricity. Furthermore, the waste heat with higher

temperature has been cooled in the ORC power plant before it is finally diverted

into treatment.

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5.1.1 Process scheme of the power plant

This ORC power plant uses typical organic Rankine cycle configuration to convert

the waste heat into electricity. The powe plant consists of boiler, turbine and

generator, condenser, and pump[Fig. 10]. Working fluid used in this power plant is

commercially available Ammonia (NH3).

Fig. 12: Process Scheme of NH3 Power Plant (Öhman, 2012 )

69 | P a g e

After the waste heat entering the power plant, heat from is transferred from the

heat source to pressurized working fluid liquid for preheating and boiling; The NH3

vapour is expanded to a lower pressure in a turbine to produce shaft work; The

output mixture of liquid and gas from turbine is condensed by the cooling water

heat sink; After condensing, the liquid is pumped back to the boiler for the required

higher pressure and then the power cycle completed. Operation of the plant is 24h

per day typically two weeks yearly maintenance.

5.1.2 Technical data of the 750 kWe power plant

Model used: Opcon ORC Powerbox Model

NPO: 750 kWe

Waste heat water in: around from 760C to 810C

Waste heat water flow rate: around 340 m3/h

Cooling water in: around from 20C to 21 0C

Cooling water flow rate: around 720 m3/h

Thermal efficiency: 8 – 9 %

5.1.3 Equipments used in this power plant

The overall sizes of the power plant are 11m in length, 4m in height, and 3,5m in

width. Total amount of the equipments of this power plant is 27,000 kg.

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Turbine:

Turbine is a key component for the operation of ORC power plant. For expansion

of working fluid, the equipment used in this ORC power cycle is Lysholm Turbine

designed and manufactured by Svenska Rotor Makiner AB, Sweden, which is a

positive displacement type, twin rotary, helical body machine (Fig. 11 below

shows the images of this particular type of Lysholm turbine):

Fig. 13: Images of Lysholm Turbine (Öhman, 2012).

The advantage of the Lysholm turbine is that its preferred operating condition is

the mixture of liquid and gas. This property allows ORC to operate without

superheating and guarantees the mechanical reliability of the turbine since

traditional diesel and gas turbine suffers from low efficiency and erosion problems

71 | P a g e

in the two phase area. The main material used for manufacturing the Lysholm

turbine is Iron.

Heat Exchangers:

Boiler and condenser are the shell and tube type of heat exchanger, those are the

most frequently used type of heat exchangers in the ORC power plants.

Working Fluid Pump:

Without furthermore information from the manufacturers, the power of working

fluid pump is 60 kWe.

Working Fluid: working fluid in this LCA analysis is Ammonia (NH3).

5.2 Life Cycle Analysis of the Power Plant

5.2.1 Goal and scope

The purpose of this study is to evaluate the environmental impacts for producing

electricity from 750 kWe ORC power plant with Ammonia as working fluid. Based

on the calculation of 210 kWe ORC power plant, the calculation results from this

750 kWe power plant will be used for another source of data considering the

72 | P a g e

environmental impact evaluations of ORC power plants. The heat source is a

typical low temperature waste heat source.

5.2.2 Functional unit

The functional unit for this study is 1 kWh electricity produced from this power

plant. This is based on the designed 30 years lifetime of power plant considering

all the energy consumed by the power plants.

5.2.3 Process flowchart of NPO 750 kWe power plant

Fig. 14: Process Flowchart of Ammonia Power Plant

ORC Power

Plant ORC Assembly

Evaporator/

Preheater

Condenser

Turbine/

Generator

Working Fluid

Pump

Raw

Material

Transport

Energy

Ammonia

Operation/

Maintenance

End‐of‐Life

Treatment

1 kWh

73 | P a g e

5.2.4 Data collection

The primary data used for LCA analysis is from the information of power plant

manufacturer, and from built-in SimaPro dataset.

5.2.5 Life cycle analysis inventory

The Life Cycle Inventory include all the inputs of ORC power plant from raw

material extraction to the end-of-life treatment.

5.3 Results

5.3.1 Total impact amounts of 750 kWe power plant

The total characterization impact amounts of chosen categories have been

calculated from the life cycle stages of the 750 kWe ORC power plant . The results

for chosen categories are listed on Table 5 below:

Table 5: Total Caracterization Impacts of 750 kWe Power Plant from

Chosen Cagegories

Categories Unit Total Amount

Climate Change kg CO2 eq 0,0009024

Ozone Depletion kg CFC‐11 eq 7,2866E‐11

Human Toxicity kg 1,4‐DCB eq 0,0009767

Photochemical Oxidant Formation kg NMVOC eq 3,5313E‐6

Particulate Matter Formation kg PM10 eq 4,3429E‐6

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Ionising Radiation kg U235 eq 0,0003073

Terrestrial Acidification kg SO2 eq 1,5383E‐5

Freshwater Eutrophication kg P eq 7,9649E‐7

Marine Eutrophication kg N eq 2,4247E‐7

Terrestrial Ecotoxicity kg 1,4‐DCB eq 1,9901E‐7

5.3.2 Life cycle stage contributions to the total amounts

The percentage contributions from the stages of assembly, operation and

maintenance, and construction and disposal have been shown on Fig. 15 below.

Fig. 15: Percentage Contributions from Life Cycle Stages of 750 kWe ORC Power

Plant

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

CC(kg CO2 eq)

OD(kg CFC‐11 eq)

HT(kg 1,4‐DCB eq)

POF(kg NMVOC)

PMF(kg PM10 eq)

IR(kg U235 eq)

TA(kg SO2 eq)

FE(kg P eq)

ME(kg N eq)

TET(kg 1,4‐DCB eq)

Evaporator/Preheater Condenser Pump Turbine/Generator WF/Ammonia

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5.3.3 Comparison between 210 kWe ORC power plant and 750 kWe ORC power

plant with NH3 as working fluid

Table 6: Comparison of characterization results from two ORC power plants

Categories Unit Total Amount Total Amount

(210 kWe) (750 kWe)

Climate Change kg CO2 eq 0,0006764 0,0009024

Ozone Depletion kg CFC‐11 eq 5,257E‐11 7,2866E‐11

Human Toxicity kg 1,4‐DCB eq 0,0009877 0,0009767

Photochemical Oxidant Formation kg NMVOC eq 2,503E‐6 3,5313E‐6

Particulate Matter Formation kg PM10 eq 2,785E‐6 4,3429E‐6

Ionising Radiation kg U235 eq 0,000182 0,0003073

Terrestrial Acidification kg SO2 eq 7,612E‐6 1,5383E‐5

Freshwater Eutrophication kg P eq 6,56E‐7 7,9649E‐7

Marine Eutrophication kg N eq 1,735E‐7 2,4247E‐7

Terrestrial Ecotoxicity kg 1,4‐DCB eq 1,380E‐7 1,9901E‐7

The results from these two ORC power plants are consistent with regard to the

working fluids for those chosen categories.

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Chapter 6

THE ENVIRONMENTAL IMPACTS OF ORC POWER PLANTS COMPARING WITH OTHER RENEWABLE TECHNOLOGIES

6.1 Comparison with Wind Power

Garrett & Rende (2012) in their paper “ Life cycle assessment of wind power:

comprehensive results from a state-of-the-art approach” have conducted with three

LCA analysis of 2-MW wind turbines. These lCAs assess all stages in the life

cycle from cradle to grace, including raw materials; production of all parts of the

wind plant; manufacturing; all transport stages; installation; operation and end-of-

life treatment. The functional unit is 1 kWh electricity produced from these

2-MW wind turbines and the software used for analysis is GaBi DfX software.

The results from this research show that for these wind turbines, to produce 1 kWh

electricity, the global warming potential is 7 to 10 g CO2 equivalent; acidification

potential 37 to 45 mg SO2 equivalent; human toxicity potential 1,150 to 1,400 mg

DCB equivalent (Garrett & Rende, 2012).

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Considering the NPO 210 kWe ORC power plant , to produce 1 kWh electricity,

the impact amount for climate change is 9,253g CO2 eqivalent; acidification

potential 26,4 mg SO2 equivalant; and human toxicity 1,4-DCB eqivalent. The

environmental impacts of these two types of power plants are at the same level of

amounts.

6.2 COMPARISON WITH HYDROPOWER

Varun, Bhat, & Prakash (2008) in their paper “Life Cycle Analysis of Run-of-

River Small Hydropower Plants in India” investigated the environmental impacts

of three small scale hydropower plants by LCA. The capacities of these three run-

of-river power plants are 50 kWe, 100 kWe, and 300 kWe , and their greenhouse

gases emissions vary from 74,88 g, 55,42 g, to 35,29g CO2

equivalent respectively for 1 kWh electricity production from these hydropower

plants. The software used in this research is EIO-LCA software. The CO2

equivalent amounts are higher than the results from ORC power plant with 1 kWh

electricity generation.

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From the above comparison and discussion, the conclusion is that the electricity

generation from ORC power plant is a promising type of energy generation

technology comparing with other renewable technologies.

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Chapter 7

CONCLUSION

The LCA evaluation of electricity generation from 210 kWe ORC power plant has

been performed in this research and the environmental impact amounts of

producing 1 kWh electricity from low-temperature waste heat ORC power plant

with R134a have been calculated. And furthermore the environmental impacts

from ORC power plants using alternative ORC working fluids scenarios have been

calculated by LCA.

The results show that from the LCA point of view, using natural substances of

NH3, CO2 and n-Pentane as working fluids in ORC power plants is more

environmentally favourable than the refrigerant working fluid R134a. And the

further investigation for the LCA environmental impact evaluation on the ORC

power plants considering power plant sizes, working fluids, etc. would be

challenging topics to do the research.

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Appendix I:

Life Cycle Inventory of NPO 210 kWe ORC Power Plant

Raw Materials

Evaporator/Preheater

Copper tube, technology mix 842,7 kg

Nickel, 99,5% 96,2 kg

Iron and steel, production mix 13,5 kg

Condenser

Steel, low‐alloyed 1142 kg

Chromium 294 kg

Nickel, 99,5% 163 kg

Pump

Stainless steel hot rolled coil, prod. mix 44 kg

Copper 14,7 kg

Turbine/Generator

Reinforcing steel 2596 kg


Chromium steel 18/8 932 kg

Copper 252 kg

Aluminium, production mix 143 kg

Iron‐nickel‐chromium alloy 76 kg

Polyethylene, HDPE, granulate 63 kg

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Working Fluid

Refrigerant R134a 1392 kg

Ammonia, liquid 1392 kg

Carbon dioxide, liquid 1392 kg

Pentane 1392 kg

Operation/Maintenance

Oil and grease 350 kg

Refrigerant R134a 1392 kg


Carbon dioxide, liquid 1392 kg

Pentane 1392 kg

Transport

Transport, passenger car 912,5 personkm

Transport, lorry > 28t 2688 tkm


Transport, freight 1296 tkm

Energy

Light fuel oil 18000 MJ

Natural gas 32130 MJ

Electricity, medium voltage 4452 kWh

Electricity, low voltage 2668 kWh

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Appendix II:

Life Cycle Inventory of NPO 210 kWe ORC Power Plant

Raw Materials

Evaporator & Preheater


Chromium 1172 kg

Nickel, 99,5% 587 kg

Condenser


Chromium 1827 kg

Nickel, 99,5% 913,5 kg

Pump

Copper 3,75 kg

Polyvinylchloride 0,45 kg

Synthetic rubber 0,105 kg

Cast iron 18 kg

Turbine/Generator

Cast iron, at plant 1000 kg

Working Fluid


89 | P a g e

Operation/maintenance

Lubricant 850 kg

Transport



Transport, passenger car 1095 personkm

Freight, rail 7498 tkm

Energy

Light fuel oil 24900 MJ

Natural gas 15300 MJ

Electricity, medium voltage 2120 kWh

Electricity, low voltage 4348 kWh

Append

Compo

Ammon

CO2 as W

CC

OD(kg

HT(kg

POF(

PMF(k

IR(k

TA

M

TET(kg

HT(kg

POF(

PMF(k

IR(k

TA

M

TET(kg

dix III:

onents Con

nia as Wor

Working F

0%

C(kg CO2 eq)

g CFC‐11 eq)

1,4‐DCB eq)

kg NMVOC)

kg PM10 eq)

kg U235 eq)

A(kg SO2 eq)

FE(kg P eq)

ME(kg N eq)

1,4‐DCB eq)

Evaporator/

0%

1,4‐DCB eq)

kg NMVOC)

kg PM10 eq)

kg U235 eq)

A(kg SO2 eq)

FE(kg P eq)

ME(kg N eq)

1,4‐DCB eq)

Evaporator/Pr

ntribution

rking Fluid

Fluid

% 10%

/Preheater

% 10%

eheater Co

n to the As

d

20% 30%

Condenser

20% 30%

ondenser Re

ssembly o

40% 50

Pump

40% 50

ecuperator

of ORC Pow

0% 60%

Turbine/Gene

0% 60%

Pump Turb

wer Plant

70% 80%

erator WF

70% 80%

bine/Generato

90 | P

t

% 90% 10

F/Ammonia

% 90% 10

or WF/CO2

a g e

00%

00%

n-Penta

CC

OD(kg

HT(kg

POF(

PMF(k

IR(k

TA

M

TET(kg

ane as Wor

0%

C(kg CO2 eq)

g CFC‐11 eq)

1,4‐DCB eq)

kg NMVOC)

kg PM10 eq)

kg U235 eq)

A(kg SO2 eq)

FE(kg P eq)

ME(kg N eq)

1,4‐DCB eq)

Evaporator/

king Fluid

% 10%

/Preheater

d

20% 30%

Condenser

40% 50

Pump

0% 60%

Turbine/Gen

70% 80%

nerator W

91 | P

% 90% 10

WF/Pentane

a g e

00%

Documents

Life Cycle Assessment of Electricity Generation from Low ... · Thomas Gibon and external contact Yves Ladam for their academic and technical guidance. Thanks to the Industrial Ecology